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Bureau of Mines Information Circular/1986 



Water-Jet-Assisted Roadheaders 



By Robert J. Timko, Bradley V. Johnson, 
and Edward D. Thimons 




UNITED STATES DEPARTMENT OF THE INTERIOR 



( J^JX^ JJ **» , (UjLW ^M ^J 



Information Circular 9108 



Water-Jet-Assisted Roadheaders 



By Robert J. Timko. Bradley V. Johnson, 
and Edward D. Thimons 




UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Hodel, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 




Library of Congress Cataloging in Publication Data: 



■00' 



Timko, Robert J 

Water-jet-assisted roadheaders. 

(Information circular ; 9108) 

Bibliography: p. 11. 

Supt. of Docs, no.: I 28.23: 9108. 

1. Mining machinery. 2. Water-jet. 3. Jet cutting. I. Johnson, Bradley V. II. Thimons, Ed- 
ward D. III. Title. IV. Title: Roadheaders. V. Series: Information circular (United States. 
Bureau of Mines ; 9108) 



TN295.U4 [TN345] 622 s [622'.24] 86-600153 



CONTENTS 



Page 



Bureau of Mines 
Information Circular 9108 



WATER- JET -ASSISTED ROADHEADERS 



Abstract 1 

2 
2 
2 
2 
6 
6 
6 

By Robert J. Timko, Bradley V. Johnson, and Edward D. Thimons ° 

8 
8 
8 
8 
9 
.0 
.1 



ERRATA 
Page 2, column 2, last line: Add "and" after "Bit wear was high," 
Page 4, column 1, second line: Delete "and." 
Page 9, column 2, line 2: Change to "an Mine in Sydney, NS (Canada)." 

Page 10, column 1, lines 36-39 should read as follows: 

3 

the 200-psi conventional pressure. In cutting 235 ft of roadway, only o 

5 bits had to be replaced at 3,000-psi water pressure, but 14 bits had / 

to be replaced when cutting a similar length of roadway at 200-psi pressure. ^ 
The use of 3,000-psi water did not reduce the machine specific ^ 

4 
Page 10, column 2: Delete last two lines, which are repeated on page 11. c 

5 
6 
6 

zies trom damage 7 

12. Water-jet-assisted Anderson Strathclyde RH22 roadheader 7 

13. Retrofitted water-jet-assisted Dosco Mk.IIA roadheader 9 





UNIT OF MEASURE ABBREVIATIONS USED 


IN THIS REPORT 


ft 


foot kW'h 


kilowatt hour 


gal/mln 


gallon per minute ym 


micrometer 


h 


hour pet 


percent 


hp 


horsepower psi 


pound per square inch 


in 


in st 


short ton 




WATER-JET-ASSISTED ROADHEADERS 



By Robert J. Timko, 1 Bradley V. Johnson, 2 and Edward D. Thimons 3 



ABSTRACT 

Water-jet-assisted cutting involves the use of a mechanical cutting 
bit in combination with a high-pressure water jet directed just in front 
of the bit tip. Such a jet can offer benefits in terms of improved cut- 
ting, reduced dust and fines, and improved bit wear. The Bureau of 
Mines, through a contract with the British National Coal Board, has re- 
searched the use of water-jet-assisted cutting on roadheaders. After 
several engineering design problems were overcome, this program led to 
the successful underground testing of these roadheaders. Today, more 
than 60 water-jet-assisted roadheaders are in operation around the 
world, and numerous others are on order. This paper details the evolu- 
tion of these machines and the benefits to be gained by their use. 

Physical scientist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA, 
2 Staff engineer, Division of Mining Technology, Bureau of Mines, Washington, DC. 
•^Supervisory physical scientist, Pittsburgh Research Center. 



INTRODUCTION 



Mining through high-compressive- 
strength rock is expensive and time con- 
suming. Two basic methods are employed: 
drilling and blasting and mechanical cut- 
ting. In many countries, the mechanical 
cutting is primarily accomplished by 
roadheaders. 

Roadheaders were first developed in 
Hungary in the 1950's and are now used 
worldwide for mining a variety of soft- 
to medium-strength materials. The Bureau 



of Mines, through a contract with the 
British National Coal Board (NCB) 
(4^), 4 has conducted research to improve 
the performance of these machines by 
equipping them with water-jet-assisted 
cutting capabilities. Based upon previ- 
ous laboratory studies, it was believed 
that this addition would result in im- 
proved cutting, reduced bit consumption, 
decreased dust and fines, and possibly 
even reduced frictional sparking. 



PRELIMINARY WATER-JET-ASSISTED ROADHEADER STUDIES 



PROTOTYPE ROADHEADER DESIGN 

The first roadheader to be modified for 
water-jet-assisted cutting was a Dosco 
Mk.IIA, which is a 24-st crawler-track 
machine capable of cutting both rectan- 
gular and arch-shaped roadways (fig. 1). 
Its cutting capacity is normally limited 
to rock with compressive strengths under 
12,000 psi. This prototype was fitted 
with a water-jet-assisted system consist- 
ing of a high-pressure pumping system, a 
rotary seal, and water-jet nozzles (fig. 
2). 

The pumping system was a hydraulically 
powered intensifier (fig. 3). It con- 
sisted of a swashplate hydraulic pump 
driven by an electric motor that de- 
livered pump-pressurized oil to the in- 
tensifier. Flexible hoses carried 2,000- 
psi oil from the pump to the intensifier. 
The pump was mounted on a sled behind the 
roadheader, and the intensifier was 
mounted on the cutting boom. High-pres- 
sure water, at a maximum flow of 12 gal/ 
min at 10,000 psi, was carried from the 
intensifier to the cutting head via 
rigid steel pipe. 

The cutting head, located at the end of 
the boom, was driven by a 65-hp electric 
motor. The boom was a turret, powered by 
hydraulic cylinders. The large, 5.5- 
in-diam cutting-head shaft required that 
the rotary seal handling the high- 
pressure water to the cutting head be 

^Underlined numbers in parentheses re- 
fer to references at the end of this 
report. 



large. The seal (fig. 4) was a BAL U- 
ring type seal, energized by an ellipti- 
cal coil spring (fig. 5). The sealing 
faces were ridged to give three sealing 
points around the circumference 
of the opening. The seals were made of 
a graphite-filled Teflon fluorocarbon 
polymer. 

The standard Dosco cutting head (fig. 
6) has bits arranged in a three-start 
helix, with seven bits on each helix. 
Two sumping bits are located at the very 
front of the cutting head. The standard 
bits and bit blocks were replaced with 
circular-shank, forward-attack bits and 
blocks to allow the water jet to be 
produced parallel to the bit tip without 
adjacent bit-block interference. Fifteen 
synthetic sapphire, high-pressure nozzles 
were installed, five on each helix. 
Since there were 21 bits on the cutting 
head, not every bit had a nozzle. The 
nozzles were countersunk into the cutting 
head to protect them from damage. They 
could be selectively capped to increase 
the water flow to the remaining nozzles. 
The nozzle-to-bit-tip standoff distance 
was 5 in (fig. 7). 

PROTOTYPE CUTTING TRIALS 

Initial cutting trials were held in 
a limestone mine in Middleton, Derby- 
shire (5). The compressive strength of 
the limestone was 17,000 psi, well 
above the normal cutting capability 
of the Dosco Mk.IIA (fig. 8). Cutting 
without the high-pressure water was 
very difficult. Bit wear was high, 






zL~t 



A 






^, _ 



FIGURE 1.— Standard Dosco Mk.MA roadheader. 



Intensifier- 



r— Hydraulic 
\ pump 




Water -jet 
nozzles- 



Rotary \ 
seal — i 



,jmi 



FIGURE 2.— Prototype NCB-modified Dosco Mk.MA roadheader showing pump and intensifies 



High-pressure 
water out 



Intensifier piston 



Nonreturn 
valve 




Water in 



High-pressure oil 



Oil reservoir 



-Hydraulic pump 
FIGURE 3.— Pumping sytem showing location of intensifier. 



-Pressure cylinder 
SeaK \ ^Seal 




FIGURE 4.— Cutting-head shaft showing location of rotary 
seals. 



Graphite-carbon-glass- fiber - 
filled Teflon body 




Polyamide 

anti-extrusion' 

ring 

FIGURE 5.— Rotary seal schematic showing coil spring. 

boom instability and bounce were prob- 
lems. The addition of and 8,000- to 
10,000 psi water-jet assist resulted in 
significant improvements. Bit wear, 
while still heavy, was greatly improved, 
and ma-chine vibration was visibly re- 
duced. The overall cutting rate was 




FIGURE 6.— Standard Dosco cutting head. 

approximately doubled, probably owing to 
proved bit wear. 

For further testing, an artificial 
sandstone heading was constructed from 
eight 3-ft sandstone cubes laid two-high 
and cemented together with shotcrete 
(fig. 9). The compressive strength of 



the sandstone was 6,500 psi. The sand- 
stone was cut with and without water-jet 
assistance. Water-jet pressures between 




FIGURE 7.— Prototype NCB-modified water-jet-assisted 
Dosco cutting head. 



6,000 and 10,000 psi were used. Flow 
rates were varied from 0.9 to 3.6 
gal/min. No reductions in machine spec- 
ific energy^ resulted due to the water- 
jet assist, probably because of the soft- 
ness of the rock. However, the 
high-pressure water did visibly eliminate 
frictional sparking and reduce dust. 

Throughout this testing, the inten- 
sifier system worked without problems, as 
did the high-pressure jet nozzles, 
although occasional unplugging of jet 
nozzles was needed. No water leakage oc- 
curred at either the nozzle-cutting head 
interface and or the cutting head-drive 
shaft interface. The only major mechan- 
ical problem involved the life of the 
rotary seal, which varied during the 
testing from a minimum of 3 h to a max- 
imum of 19 h. Because the seal is located 
in the cutting boom, each seal change 
caused considerable downtime. To deal 
with this problem, the NCB rede- 
signed the seal to reduce its size. A 
cartridge assembly was developed that 
incorporated a small-diameter, readily 
accessible, easy-to-change BAL seal with 
a graphite-carbon-glass fiber-filled Tef- 
lon body. To install the seal in the 
boom, a layshaft gearbox was placed into 

-"Machine specific energy is the energy 
consumed by the machine without consider- 
ing the energy required to supply the 
high-pressure water. 




FIGURE 8.— Dosco Mk.HA roadheader preparing to cut Middleton limestone using water-jet assist. 




3-ff-cube 
sandstone blocks (8) 



Rock 
pillar 



Gap between blocks 

and rock face 
filled with shotcrete 



FIGURE 9.— Schematic diagram of artificial sandstone 
heading. 



Layshaft gearbo 
Cutting-head shaft 
-Cutting-head 



Epicyclic gearbox 




Water passage 



Smail-diameter rotary seal 



FIGURE 10.— Section through layshaft gearbox showing 
location of U-ring seal. 



the boom in front of the cutting-head 
shaft (fig. 10). Laboratory tests with 



this new seal showed that a seal 
over 900 h could be expected. 



life of 



PREPRODUCTION WATER-JET-ASSISTED ROADHEADER RESEARCH 



Following the prototype research de- 
scribed above, roadheaders were retro- 
fitted with water-jet-assist capabilities 
by NCB and by two machine manufacturers, 
Dosco and Anderson Strathclyde. Each 
machine was evaluated separately in 
underground trials. 

NATIONAL COAL BOARD MODIFIED DOSCO 
ROADHEADER 

Description 

The NCB made several modifications to 
its prototype Dosco Mk.IIA roadheader. 
The oil-water intensifier, which provided 
a maximum flow rate of 12 gal/min at 
10,000 psi, was powered by a swashplate 
hydraulic pump mounted on the rear of the 
machine. A valve assembly allowed the 
operator to select 10,000-psi water for 
harder strata or 2,000-psi water in soft- 
er rock for dust suppression only. The 
layshaft gearbox was installed in the 
boom. Water was plumbed from the 
intensifier, through the rotary seal, to 
the cutting head. 

Tungsten carbide water-jet nozzles 
were installed on the cutting head; but 
unlike those on the prototype roadheader, 
these nozzles were raised above the 
cutting-head body to reduce the standoff 



distance from nozzle to bit tip to 3.5 
in, creating a more concentrated water 
jet. To protect the nozzles from damage, 
they were surrounded by steel shrouds 
(fig. 11). Supply water was filtered to 
40 ym. 

The water-jet system was interlocked 
with the roadheader's electric and hy- 
draulic systems. In this way, the high- 
pressure water could only be turned on 
when the cutting head was running. 

Cutting Trials 

In the underground test, this machine 
cut a 240-ft-long entry in sandstone hav- 
ing a compressive strength of 13,000 psi. 
At 10,000-psi water pressure, bit life 
was doubled compared with that achieved 
using conventional cutting at lower water 
pressure. Significant dust reductions 
were seen up to about 3,000-psi water 
pressure with no additional improvement 
above that pressure. No frictional 
sparking was observed when the high- 
pressure water was on, but did occur when 
it was off. Unfortunately, no machine 
specific energy measurements were made 

O). 

Because the boom-mounted intensifier 
obstructed the operator's vision, it was 
remounted on the roadheader mainframe 



with a shrouded flexible hose carrying 
water to the boom. The intensifier 
worked flawlessly. Contamination pro- 
blems did occur in the hydraulic power 
pack that drove the intensifier, but 



regular flushing and filter changes rec- 
tified them. Debris in the water supply, 
even with the 40 ym filtration, caused 
repeated nozzle plugging, but the nozzles 
could be quickly cleaned with a twist 
drill bit. 




FIGURE 11.— NCB-modified Dosco cutting head showing 
steel shrouds used to protect nozzles from damage. 



MODIFIED ANDERSON STRATHCLYDE ROADHEADER 

Description 

The Anderson Strathclyde RH22 is a 
medium-weight crawler-track machine that 
weighs 37 st and is usually limited to 
cutting rock with compressive strengths 
less than 14,000 psi (fig. 12). This 
machine was modified for water-jet assist 
by installing a triplex pump and header 
tank on the rear of the machine, behind 
the operator seat. Maximum water- 
pressure capability was 14,500 psi, but 
the pressure was limited by a relief 
valve to a maximum of 10,000 psi for safe 
operation. Water flow and output pres- 
sure could be varied from 4.7 5 gal/min at 
580 psi to 19.8 gal/min at 10,000 psi by 



Triplex 
pump 



Header 
tank-. 




FIGURE 12.— Water-jet-assisted Anderson Strathclyde RH22 roadheader. 



maneuvering a single joystick located at 
the operator position. 

The RH22 boom contained an axial water 
passage with a small-diameter rotary seal 
at the motor end. Because the boom tele- 
scopes, a sliding seal was built into the 
water passage on the cutting-head end. 
High-pressure water was fed to the cut- 
ting head through a flexible hose, which 
was shrouded for safety by a second, 
larger diameter flexible hose. The cut- 
ting head was a standard RH22 cutting 
head with tungsten carbide high-pressure 
nozzles installed in front of each of the 
24 bits. 

Cutting Trials 

This RH22 water-jet-assisted roadheader 
was tested in the Sutton Manor Colliery, 
where it was used to drive a 1,150-ft 
entry in rock of compressive strength up 
to 24,000 psi. Operating at 10,000 psi, 
water-jet assist resulted in a 50-pct in- 
crease in advance rate over normal oper- 
ation at 100 psi (_]_)• There was a de- 
crease in machine specific energy of 
about 30 pet, although the total specific 
energy^ actually increased when the pump- 
ing energy was considered. A respirable 
dust reduction of 70 pet occurred as the 
water pressure was raised from 100 psi to 
3,000 psi. Additional increases in water 
pressure had no effect on dust levels. 
Machine vibration was visually reduced, 
and no frictional sparking was evident 
when the high-pressure water was used. 
Significant reductions in bit wear oc- 
cured. At 10,000 psi, bit wear was as 
low as 0.20 bit/ft of advance as compared 
to normal bit wear of 0.83 bit/ft of ad- 
vance. The greatly improved bit wear may 
have been responsible for much of the in- 
crease in advance rate. 

A bit longevity experiment was per- 
formed by plugging one of the front jet 
nozzles. In cutting an advance of ap- 
proximately 3 ft, the bit that received 
no water owing to the closed nozzle had 
to be replaced three times, while only 
one other bit on the entire cutting head 
had to be replaced. 

"Total specific energy is energy re- 
quired to supply high-pressure water plus 
the machine specific energy. 



Overall, this machine performed well 
during the cutting trials. A few prob- 
lems did occur. The sliding seal on the 
telescoping boom failed and had to be re- 
designed in order to improve its durabil- 
ity. Additionally, nozzles frequently 
became plugged owing to impurities in the 
water supply, but these orifices were 
easily cleaned with twist drills having 
the same diameter. 

RETROFITTED DOSCO ROADHEADER 

Description 

Dosco retrofitted an Mk.IIA roadheader 
with a water-jet-assist system similar to 
that used on the NCB prototype, except 
that the water pump was installed on the 
roadheader frame (fig. 13). Dosco used 
the NCB-developed layshaft gearbox with 
its small-diameter seal. The high- 
pressure water was delivered to the cut- 
ting head via rigid steel pipe with hori- 
zontal and vertical articulating joints 
to accommodate movement of the boom. 
Synthetic sapphire, water-jet nozzles 
were supplied in front of the bits on the 
standard Mk.IIA hardrock cutting head 
(2). 

Cutting Trials 

This machine was tested in the Bentinck 
Colliery where the strata ranged from 
soft mudstones to hard laminated sand- 
stones, having compressive strengths ap- 
proaching 20,000 psi. It was used to en- 
large an existing roadway. Floor water 
problems resulted in the high-pressure 
water being used only intermittently, and 
conclusive data on its performance were 
not obtained. 

Several mechanical problems with the 
rotary seal did develop. Owing to metal- 
lic contamination of the water supply, 
the rotary seal eroded and failed after 
very short periods of use. This problem 
was overcome by using impoved hydraulic 
components. Additionally, the high 
cyclic loading generated by the eight- 
cylinder pump and the rigid steel pipe 
caused another failure of the rotary 
seal. This problem was solved by re- 
placing the eight cylinder pump with 



Water-jet -assiste 
cutting head- 




Hydraulic 
pump 

FIGURE 13.— Retrofitted water-jet-assisted Dosco Mk.llA roadheader 



a four-cylinder version and substituting 
flexible hose for the steel pipe (6). 
With these modifications, the rotary seal 



was able to operate for approximately 
900 h before breakdown. 



CURRENT WATER-JET-ASSISTED ROADHEADER STATUS 



Both Anderson Strathclyde and Dosco now 
commercially market water-jet-assisted 
roadheaders. More than 60 of these ma- 
chines are operating around the world, 
and many more are on order. They are 
available in a variety of machine weights 
and have water-jet-assist capabilities 
ranging from 2,000 to 10,000 psi. In ad- 
dition, Dosco offers a water-jet-assist 
retrofit system for roadheaders that al- 
ready have a water lance through the 
boom. The average price of the retrofit 
system is about $75,000. 

Currently, three Dosco Mk.IIB and two 
Anderson Strathclyde RH22 water-jet-as- 
sisted roadheaders are in operation at 



the Cape Breton Development Corp. 's Phel- 
an Sydney, NS (Canada). These roadhead- 
ers are cutting five parallel develop- 
ment drifts on a 16° slope. Some mech- 
anical problems, such as leaking seals 
and plugged water-jet sprays, have occur- 
red but overall performance has been 
good and the mine has ordered two more 
water-jet-assisted machines. These will 
be low-profile Dosco L-1300 roadheaders 
with 3,000-psi water-jet capability. 
Dust measurements made by the Canada 
Centre for Mineral and Energy Technology 
(CANMET) on the roadheaders at this mine 
showed dust reductions as much as 80 pet 
greater than conventional spray systems 



10 



with 3,000-psi water pressure; no further 
reductions occurred as the pressure was 
increased above this level. At 10,000 
psi, there was no increase in cutting ad- 
vance rate when cutting rock or coal. 

Both Dosco and Anderson Strathclyde now 
feel that for many mining operations, es- 
pecially in softer materials, water pres- 
sures well below 10,000 psi will be 
sufficient to gain the benefits of 
water-jet-assisted cutting in terms of 
dust reductions, bit wear improvements, 
f rictional-sparking reductions, and de- 
creased fines. Lower pressure machines 
will also entail fewer engineering design 
problems, cost less, and be safer and 
more economical to operate. 

Dosco recntly supplied a medium- 
pressure water-jet-assisted Mk.IIB road- 
header to the Beringen Mine in Belgium. 
This machine was specially designed to 
deliver a maximum water-jet-assist pres- 
sure of 3,000 psi. In place of the large 
electric motor and pump required for 
10,000-psi operation, this machine em- 
ploys a compact three-cylinder positive- 
displacement hydraulic pump capable of 
supplying 10.5 gal/min at 3,000 psi. The 
water is delivered to 20 of the 24 cut- 
ting bits. For approximately 6 months, 
this roadheader has been cutting coal 
having banded rock intrusions with com- 
pressive strengths of 14,000 psi. At 
3,000-psi water pressure, respirable dust 
was reduced by 75 pet from its level at 
the 200-psi conventinal pressure. In 
cutting 235 ft of roadway, only 5 bits 
had to be replaced at 3,000-psi water 
did not reduce the machine specific 



energy, indicating that no cutting-force 
reductions occurred. In fact, there was 
a slight increase in total specific en- 
ergy due to the energy required to supply 
the 3,000-psi water. 

An Anderson Strathclyde RH22 roadheader 
with 5,000-psi water-jet assist has been 
successfully operating at the Kellingly 
Colliery in North Yorkshire. Cutting 
dry, an average of 60 bits per day had to 
be replaced, but at 5,000 psi, the aver- 
age was only 24. Although no dust mea- 
surements have been made, there was 
a significant visual reduction in dust 
when the 3,000-psi water was used. 

Currently, research is being done by 
NCB and by Bergbau Forschung of the 
Federal Republic of Germany to determine 
the effect of higher water-jet-assisted 
cutting pressures (20,000 psi and above) 
on roadheaders. While major reductions 
in dust and bit wear can be achieved at 
lower pressures, it is believed that much 
higher pressures are needed to have a 
significant impact on cutting forces. 
The West Germans have demonstrated that, 
as the water pressure on a roadheader was 
raised from to 21,000 psi, the machine 
energy consumption fell from 130 to 85 
kW*h. However, the total energy consumed 
increased from 130 to 310 kW*h. Thus, 
the cost of operating at these higher 
pressures is significant. The West 
Germans are willing to accept this if 
it makes it possible for them to effec- 
tively cut the high-compressive-strength 
rock they encounter in their mining 
operations. 



SUMMARY 



Testing of water-jet-assisted road- 
headers has shown that significant respi- 
rable dust reductions occur at pressures 
approaching 3,000 psi. Raising the water 
pressure above that level has no effect 
on dust reduction. Improved bit wear and 
reduced frictional sparking also result, 
but the optimum water pressures to ob- 
tain these benefits are not as clearly 
defined. 

A reduction in machine specific energy 
(improved cutting) was also seen in the 
cutting of harder materials, but was not 



evident in the cutting of lower- 
compressive-strength materials such as 
coal and soft rocks. However, the total 
specific energy always increased owing to 
the energy required to supply the high- 
pressure water to the nozzles. 

More than 60 water-jet-assisted road- 
headers are in operation worldwide, and 
several others are on order. These have 
water-jet pressure capabilities ranging 
from 2,000 to 10,000 psi. Currently, 
European researchers are concentrating 
their efforts on studying the effects of 



11 



European researchers are concentrating 
their efforts on studying the effects 
of water-jet assist on high-compressive- 



strength materials by using 
pressures of 20,000 psi and abave. 



water 



REFERENCES 



1. Clark, R. A. Success for Anderson 
Strathclyde High-Pressure-Water Road- 
header. Colliery Guardian, July/Aug. 
1984, pp. 255-256. 

2. Colliery Guardian. Dosco "Experi- 
ence of High Pressure Water Assisted Cut- 
ting Trials at Bentinck Colliery." July/ 
Aug. 1984, pp. 258-259. 

3. Erhart, P. P. Water-Jet-Assisted 
Cutting Nears Commercialization. Coal 
Min. , v. 21, No. 12, 1984, pp. 55-59. 

4. Mining Research and Development Es- 
tablishment, National Coal Board, Tun- 
nelling and Transport Branch. Water Jet 
Assisted Roadheader. Ongoing BuMines 
contract J0133929; for inf., contact R. 



J. Timko, TPO, Pittsburgh Research 
Center, BuMines, Pittsburgh, PA. 

5. Plumpton, N. A., and M. G. Tomlin. 
The Development of a Water Jet System To 
Improve the Performance on a Boom Type 
Roadheader. Paper in 6th International 
Symposium on Jet Cutting Technology 
(Univ. Surrey, United Kingdom, Apr. 6-8, 
1982). BHRA Field Eng. , Cransfield, Bed- 
ford, United Kingdom, 1982, pp. 267-282. 

6. Straughan, J. High Pressure Water 
Jet Applications to Roadheaders. Paper 
in Proceedings 3rd U.S. Water Jet Con- 
ference. (Univ. Pittsburgh, Pittsburgh, 
PA, May 21-23, 1985). Univ. Pittsburgh, 
Pittsburgh, PA, 1985, pp. 194-213. 



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